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321.
The electron ionization mass spectra of five series of seven 2-aryl,4-R-substituted (R = Me, Et, i-Pr, t-Bu or Ph) 3,4,5,6-tetrahydro-2H-1,3-oxazines were recorded at 14 and 70 eV in order to study the ring-chain tautomeric equilibria in the gas phase. Certain fragment ions were associated with the ring or with the open-chain forms of the compounds. As in chloroform solution, the electron-withdrawing effect of the aryl substituent (p-NO(2), m-Br, p-Cl, H, p-Me, p-OMe and p-NMe(2)) shifts the equilibrium towards the ring form. The correlation of ring-chain equilibria (log K = [ring]/[chain]) with the Hammett sigma+ constants of the aryl substituents was in general good or satisfactory although in some cases the p-NMe(2) did not fit these correlations. 相似文献
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Szabolcs Matkó Sándor Keszei István Csontos Péter Anna György Marosi Miklós Zsuga Jenő Borda Gábor Nagy 《Macromolecular Symposia》2006,233(1):217-224
In this work we aimed at forming partially recycled polymer composites of appropriate mechanical properties and flame retardancy. Multilayer composite structures proved to be suitable to fulfill all of these requirements. Core-shell structures presented here contain two-component thermosets, i.e. epoxy, recycled polyurethane and polyisocyanurate, as matrices reinforced with waste fillers such as short basalt fibers and wood chips. Flame retardancy and mechanical properties of the core-shell structures were investigated by the conventional methods of characterization. The developed cost-effective multilayer composites can be applied as heat and sound insulating panels e.g. multifunctional sheets for construction or automotive industry. 相似文献
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Zoltán Gombos Veronika Nagy Eva Koštáková László Mihály Vas 《Macromolecular Symposia》2006,239(1):227-231
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Martinek TA Hetényi A Fülöp L Mándity IM Tóth GK Dékány I Fülöp F 《Angewandte Chemie (International ed. in English)》2006,45(15):2396-2400
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Krisztina Sebk‐Nagy Lszl Biczk Akimitsu Morimoto Tetsuya Shimada Haruo Inoue 《Photochemistry and photobiology》2004,80(1):119-126
Effects of solvent, pH and hydrogen bonding with N‐methylimidazole (MIm) on the photophysical properties of 1‐hydroxyfluorenone (1HOF) have been studied. Fluorescence lifetime, fluorescence quantum yield and triplet yield measurements demonstrated that intersystem crossing was the dominant process in apolar media and its rate constant significantly diminished with increasing solvent polarity. The acceleration of internal conversion in alcohols paralleled the strength of intermolecular hydrogen bonding. The faster energy dissipation from the singlet‐excited state in cyclohexane was attributed to intramolecular hydrogen bonding. The pKa of 1HOF decreased from 10.06 to 5.0 on light absorption, and H3O+ quenched the singletexcited molecules in a practically diffusion‐controlled reaction. On addition of MIm in toluene, dual fluorescence was observed, which was attributed to reversible formation of excited hydrogen‐bonded ion pair. Rate constants for the various deactivation pathways were derived from the combined analysis of the steady‐state and the time‐resolved fluorescence results. 相似文献
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In this paper, using recent results in finite geometry, we study a certain class of 2-level shared secret schemes. We shall present upper bounds on both the number of participants in total and on the number of participants in the lower level, which constitute the only nontrivial cases, and construct examples for the extremal cases. 相似文献